1. Field of the Invention
This invention relates to the construction of an electro-luminescent (EL) strip, and to a connector arrangement for an EL strip which permits "do-it-yourself" connection of the EL strip to a power source without the need for special skills or tooling.
2. Discussion of Related Art
EL strips are used in a wide variety of products for the purpose of enhancing their safety and attractiveness. Because they are thin, lightweight, flexible, and can be easily attached to different surfaces by adhesives or by stitching, they are ideal for use on clothing, including safety vests, belts, caps, and shoes, as well as on such diverse items as bags and vehicles. The relative brightness of the light generated by such strips, the availability of multiple colors, and the wide viewing angle allow EL strips to serve as replacement for the number of conventional light sources, including LEDs, fluorescent tubes, and gas discharge lamps, as well as ordinary incandescent bulbs.
One application for which practical problems have prevented the widespread adoption of EL strips is window or storefront signage. Although comparable in performance for neon tube lighting, current EL strips are too expensive for this application, both in terms of manufacturing costs and because the conventional EL strip packages are difficult to customize and install. This inflexibility is also a limitation in the more traditional applications, where it would also be desirable if the EL strips could be more easily cut and arranged by the customer, rather than requiring that the EL strips be manufactured in advance to particular design specifications. The present invention addresses this problem as well as the problem of cost, which is also a factor in limiting the more widespread use of EL lighting.
A conventional EL strip is operated by applying a high and a low voltage to opposite poles of a chemical layer, conventionally a phosphor, the poles being isolated to thereby create a voltage potential and a resulting electric field across the phosphor, and by varying the voltage at a characteristic excitation frequency which causes the phosphor to emit light phosphor.
FIGS. 1-4 illustrate the arrangement and principles of operation of a conventional EL strip. As shown in FIG. 1-A, the conventional EL strip or panel is made up of a transparent conductive layer, a phosphor layer, an isolation layer, a reflective layer, and a conductive layer. FIG. 1-G shows the voltage drop or energy potential between the conductive and the transparent conductive layers, which is necessary to cause the phosphors to emit light energy. The brightness of the light emitted by the strip depends on the voltage applied to the phosphor layer and upon the electrical frequency. In general, the higher the voltage and the higher the frequency, the brighter the panel. The different colors can be produced by an appropriate choice of phosphors, and color can be varied for a particular phosphor by changing the frequency of the applied voltage, with increasing frequency shifting the color towards the blue end of the spectrum.
The above-noted problems with this arrangement, i.e., difficulties in manufacture and implementation, are related to one of its principal advantages, namely its lack of thickness, which results in its light weight. In the illustrated arrangement, the transparent conductive layer typically has a thickness of 5 microns, the phosphor layer has a thickness of 10-150 microns, the isolation layer has a thickness of 5-100 microns, the reflective layer has a thickness of 4-10 microns, and the lower conductive layer has a thickness of 12-20 microns, for a total thickness of 36 to 280 microns or 0.036 to 0.280 inches. This lack of thickness in comparison with conventional lighting sources is one of the reasons EL strips are so attractive, but because the conventional EL panel is so thin, it is very difficult to attach terminals in order to the respective top and bottom conductive layers.
More specifically, the problem is that, if the terminals are aligned vertically, then it is impossible to prevent short circuits across the space separating the terminals, and in addition attaching wiring to the terminals is extremely difficult in such a narrow space, and thus it is conventional during manufacture to displace the upper and lower terminals laterally in the direction of arrow X, shown in FIG. 2-D by extending the width of the upper transparent conductive layer so that the terminals are no longer above one another, decreasing the danger of short circuits and leaving more room for attachment of wires to the terminals.
Although this configuration, solves some of the problems of terminal design, it has the disadvantage of preventing a uniform appearance, as is apparent from the top view shown in FIG. 2-A in which (a) represents the width of the extended portion of the transparent conductive layer, (b) represents the width of the remainder strip, (c) represents the width of the combined structure, and (d) the width of a practical terminal. In general, the width of the extended layer is one-tenth that of the remaining five layers, or 1-2 mm, as illustrated in FIG. 2-C. Furthermore, in order to reinforce the extended portion of the transparent conductive layer, and protect the transparent conductive layer from destruction due to high voltages while maintaining the necessary voltage potential between the top and bottom conductive layers, it is conventional to add a reinforcing layer of conductive adhesive, thereby increasing the cost of the strip.
The situation thus arises, in the conventional arrangement, that the easier it is to make the necessary electrical connections, due to an increase in width of the transparent conductive layer, the less attractive and higher cost of the resulting strip. While it is possible to save costs by including reinforcement in only half of the transparent conductive layer, as shown in FIG. 2-B, the resulting performance is significantly diminished.
The EL strip of the present invention, in contrast, does away with the conventional terminals and instead provides a parallel vertical configuration which simplifies electrical connections, allows the strip to be cut to any desired width, and provides a more uniform and attractive appearance. Instead of combining the transparent conductive layer represented in FIG. 1-B with the conventional arrangement shown in FIG. 1-D, the invention combines the structure shown in FIG. 1-C, in which the reflective layer is deleted but the necessary conductive and isolation layers are still included, with the conventional arrangement in a side-by-side configuration. In this arrangement, the silver-based conductive adhesive used in the conventional extended layer is not needed, reducing costs, while at the same time eliminating the non-lighted portion of the strip and providing good isolation between the terminals.